134 THE KINGDOM OF MAN 



Metschnikoff the zoologist and embryologist that we 

 owe the doctrine of phagocytosis and the consequent 

 theory of immunity now so widely accepted. 



We must not forget that in this same period much 

 of the immortal work of Pasteur on hydrophobia, of 

 Behring and Roux on diphtheria, and of Ehrlich and 

 many others to whom the eternal gratitude of mankind 

 is due, has been going on. It is only some fifteen years 

 since Calmette showed that if cobra poison were intro-. 

 duced into the blood of a horse in less quantity than 

 would cause death, the horse would tolerate with little 

 disturbance after ten days a full dose, and then day 

 after day an increasing dose, until the horse without 

 any inconvenience received an injection of cobra poison 

 large enough to kill thirty horses of its size. Some of 

 the horse's blood being now withdrawn was found to 

 contain a very active antidote to cobra poison what is 

 called an antitoxin. The procedure in the preparation of 

 the antitoxin is practically the same as that previously 

 adopted by Behring in the preparation of the antitoxin 

 of diphtheria poison. Animals treated with injections of 

 these antitoxins are immune to the poison itself when 

 subsequently injected with it, or, if already suffering 

 from the poison (as, for instance, by snake-bite), are 

 readily shown by experiment to be rapidly cured by 

 the injection of the appropriate antitoxin. This is, as 

 all will admit, an intensely interesting bit of biology. 

 The explanation of the formation of the antitoxin in 

 the blood and its mode of antagonising the poison is not 

 easy. It seems that the antitoxin is undoubtedly formed 

 from the corresponding toxin or poison, and that the 

 antagonism can be best understood as a chemical 

 reaction by which the complex molecule of the poison 

 is upset, or effectively modified. 



